Earth Surface Processes

Question 1

Define WEATHERING, both PHYSICAL and CHEMICAL

Answer 1

The in-situ breakdown of primary solid phases into its constituent parts.
Physical weathering results in reduced grain size
Chemical weathering is from chemical reactions, which can result in solutions or gases

Question 2

4 types of physical weathering

Answer 2

• Pressure releases as the rock is uplifted and exposed. It springs apart along planes of weaknesses (joints).
• Insolation weathering - due to thermal expansion and contraction since rock has a poor heat conductivity and minerals can expand differently - stresses between surface and interior, and between grains
• Hydration weathering - water absorption can cause swelling and therefore weakness of rocks like clays
• Frost weathering - water in the cracks changes to ice and expands. A similar processes can occur with salts or even tree roots.

Question 3

4 types of chemical weathering

Answer 3

Carbonate weathering - carbonic acid dissolving carbonates and transfers them to oceans
Silicate weathering - carbonic acid causing substitution of carbonate ion into silicate ion
Oxidation - for example when iron-rich minerals go to hematite
Biochemical weathering when plants take in nutrients.

Question 4

What is Goldlich’s series?

Answer 4

Shows the stability of different rock compositions, from olivine and calcium feldspar to quartz being the most stable.

Question 5

What is a REGOLITH?

Answer 5

the unconsolidated layer of solid material over the bedrock. its thickness is a function of climate.
an example of how it can be affected is if tectonic uplift is much quicker than soil production, hence thinning the regolith.

Question 6

What is DENUDATION and what are the types?

Answer 6

Denudation is a geological process that involves the removal of sediment or rock from a particular area due to the action of natural forces such as erosion, weathering, and mass wasting.
Physical denudation is when sediment is carried through clastics
Chemical denudation is when sediment is dissolved

Question 7

What is the stream power equation

Answer 7

Ω=ρgQS
Q = volume of water flow
S = slope

Question 8

Types of sediment deposits

Answer 8

Clastic e.g. breccia, sandstone
Biogenic e.g. limestone, coal
Chemical e.g. evaporites
Volcaniclastic e.g. tuff

Question 9

How are grains classified?

Answer 9

• Size - Wentworth grain scale
• Angularity/Sphericity
• Matrix- or grain-supported
• Texturally mature (high matrix pct) or immature (low matrix pct)
• Compositional maturity - how stable it is i.e. qtz is most stable

Question 10

Clast composition: Quartz

Answer 10

• Hard, no cleavage.
  
  • Average sandstone is mainly quartz
  • Often several cycles of deposition/erosion
  • Predominantly derived from granite or gneiss

Question 11

Clast composition: Feldspars

Answer 11

• Less hard due to cleavage
  
  • Chemically labile, replaced by clay minerals
  • Typically derived from continental basement, and so an indicator on source.
    Intense weathering leads to breakdown.

Question 12

Clast composition: Lithic Fragments

Answer 12

• Important in conglomerates, breccias, coarse sandstones
  
  • Type depends on the source
  • Crystallinity/grain size are always less than the grain size of sediment.

Question 13

Clast composition: Micas & Clays

Answer 13

• Common in matrixes.
  
  • Derived from metamorphic/igneous sources
    
    • Clay minerals are products of weathering or authigenic (in situ) formation

Question 14

What is the Pettijohn classification?

Answer 14

Classifies sandstones on 4 axes:
- triangle of qtz-feld-lf
- 4th axis on pct matrix

Question 15

Define DIAGENESIS

Answer 15

The physical and chemical changes that alter the characteristics of a sediment after deposition. It changes unconsolidated sediment into rock, starting immediately after deposition.

Question 16

What are some things that occur during diagenesis?

Answer 16

It can alter primary minerals.
It decreases pore space
Cements can precipitate - friable means weakly; indurated means strongly
Concretions can occur where cements accrete around a nuclei

Question 17

What does the Hjülstrom diagram show?

Answer 17

Which of erosion, transport or deposition will occur at a given flow velocity and grain size. Clays are harder to erode than would be expected due to cohesive forces.

Question 18

What are some depositional sedimentary structures

Answer 18

Beds/laminations
Ripples/Dunes - showing flow direction and having X-bedding over time

Question 19

What are some erosional sedimentary structures

Answer 19

Flute marks where eddies or objects erode the bed
Tool marks like grooves and bounce marks
Channels formed by rivers

Question 20

What are some post-depositional sedimentary structures

Answer 20

Convolute bedding and sand volcanoes can result from dewatering
Load casts and flame structures can result from density differences

Question 21

What environments do deserts form?

Answer 21

• Around 30o or 90o due to cell convections causing high pressure
• In rain shadows, like the Patagonian over the Andes
• Continental deserts where air has travelled so far that moisture is lost, like Gobi

Question 22

How can wind ripples differ from water ripples

Answer 22

Wind structures are often much bigger.
Wind direction can change more, so different shapes can be created.

Question 23

3 Types of Lake

Answer 23

Hydrologically closed (and open) - where the only way out is evaporation
Saline - low rainfall, high evaporation
Ephemeral - periodically drying out, leading to dessications.

Question 24

Types of lake sediment

Answer 24

Siliclastic - from rivers and streams. Laminations can get preserved well due to anoxic conditions in stratified lakes
Biochemical - from organisms e.g. carbonates

Question 25

What are ALLUVIAL FANS?

Answer 25

Cones of material formed at the break of a slope on the edge of an alluvial plain.
Common in semi-arid regions where water flow is irregular.

Question 26

Types of river

Answer 26

Straight

Braided - favoured in high gradient areas. fluctuating discharge, coarse load with high bedload. Bars form that can migrate and cause X-laminations

Meandering - favoured in low gradient areas. Defined by thalweg. Steady discharde, low bedload. Point bars build up on inner banks.

Anastomosing - made of many major stable channels, permanent islands.

Question 27

What is the Galloway diagram?

Answer 27

Classifies deltas based on the dominance of wave, tidal and fluvial processes.

Question 28

How do fossils and sediment change with marine depth?

Answer 28

sediment gets more rounded and well sorted with depth.
Deeper waters have less fossil diversity, and burrowing changes from vertical burrows in the littoral zone to networks in the Neritic zone, getting shallower.

Question 29

What are turbidity currents?

Answer 29

Characterised by the Bouma sequence, turbidity currents are massive downhill marine flows caused by density differences. they are triggered by earthquakes, collapses etc.
Deposits are characterised with coarse layers, with parallel laminated and then cross-bedded sand, then with the standard mud on top. Bioturbations only appear in the mud.

Question 30

What is limestone? What are ooids, micrites and sparites?

Answer 30

Where there is no sediment supply, carbonate rocks form from calcifying organisms (biogenic) or from precipitation.

Ooids are spherically-eroded grains formed in warm, agitated waters.

Micrites have a calcite matrix.

Sparites are crystalline looking, forming during diagenesis as cement

Question 31

How are Limestones classified?

Answer 31

Folk - based on sparite vs micrite, then through the clast composition,

Dunham - based on grain size, distribution and composition.

Question 32

What are controls on carbonates?

Answer 32

Isolation - sediment inhibits carbonate production
Shallow, clear, warm water with normal salinity - to allow for the right organisms to live
Geological age - different organisms formed ancient reefs

Question 33

Describe a reef facies:

Answer 33

Fore reef - mainly redeposited sediments brought down from the reef core.
Reef core - comprising the organisms in situ, like bivalves, corals, sponges. No obvious stratification. Coral takes different forms at different points.
Back reef - some skeletal debris, much finer grained carbonate.

Question 34

How do siliceous and carbonate sediments get deposited?

Answer 34

They are fine grained ooze upon deposition, which is pressurised to a limestone.

Question 35

How does deep sea clay get deposited?

Answer 35

It is mostly wind-blown.

Question 36

What organisms produce carbonates and silicates in deep ocean?

Answer 36

Carbonate examples include coccolithophorids (Triassic phytoplankton), planktonic foraminifera (Jurassic zooplankton).

Silicate examples include diatoms (unicellular Cretaceous phytoplankton) and radiolarians (Cambrian zooplankton). The biogenic opal that is formed is metastable, so converts into quartz (chert, which is a microcrystalline quartz) easily once the organism dies.

Question 37

How can alluvial fan sediments be identified?

Answer 37

Due to the flow losing energy quickly, the sediment deposited becomes well-sorted, but stay angular due to short travel distance.
Due to the slope of the alluvial fan, if a vertical borehole is taken, the material gets coarser as you go up.

Question 38

How can desert sediment be recognised

Answer 38

Red - Fe3+ - oxidising environment
Dune-scale x-beds and ripples
Low biodiversity of fossils
Sediment is small and well sorted and compositionally mature
Desiccations, evaporites

Question 39

Where does each carbonate/silicate organism dominate?

Answer 39

Phytoplankton need light to photosynthesise, with diatoms dominating in areas of high-nutrient, high latitude regions and coccolithophorids are most abundant in warm areas controlled by light.
Zooplankton dominate in the other areas, with radiolarians being rare outside warm regions and foraminifera ranging from the equator to polar regions.